The present invention relates to an apparatus for the remote examination of faults or defects emerging on the inner surface of a deep cavity. More specifically, said apparatus utilizes the photoluminescence of a so-called penetrating substance, which is selectively fixed in or on the surface defects of the deep cavity.
Among the presently most widely used methods for investigating surface faults or defects on mechanical parts and particularly on tubes, reference can more particularly be made to gammagraphy, neutronography, ultrasonics, eddy currents and dye penetrant inspection.
The latter method is widely used for investigating faults emerging on the surface and whose small size does not make it possible to observe them with the naked eye. The principle of dye penetrant inspection is as follows. The area to be observed is impregnated with a liquid having a high penetrating power and which contains tracers becoming fluorescent when they are excited by an ultraviolet light.
The defects emerging on the surface and no matter what their size, are filled with this liquid and form microreservoirs. This liquid or penetrant is then eliminated from the surface by rinsing e.g. with water.
Certain of these liquids, called auto-penetrants, as a result of interfacial tension and adsorption phenomena, reappear on the surface after a certain time, thereby revealing microdefects within which they had infiltrated by the emission of an intense, bright light when illuminated by ultraviolet light.
The first apparatuses using ultraviolet radiation for investigating faults and defects had mercury vapour or black light lamps, whose dimensions were to large to permit their introduction into small cavities, such as small diameter tubes. An attempt was made to use miniaturized lamps incorporated into the end of endoscopes. However, such apparatuses suffered from the disadvantages that they had a low illuminating power and gave off a large amount of heat.
An attempt was also made to use light guides, either in the form of glass fibres, or in the form of liquids. However, for wavelengths between 380 and 400 nanometers, these different guides do not make it possible to exceed a luminous flux of 2000 microwatts/cm.sup.2 at a distance of a few meters, which limits the use of this illumination process.